The present invention generally relates to an automatic transmission.
Recently, many automatic transmissions installed in vehicles are multi-speed automatic transmissions that have, for example, eight forward speeds. In addition, from the standpoint of convenience in assembling transmissions into vehicles, there has been a demand that many of the component parts, such as clutches, should be arranged in a compact manner in each automatic transmission.
There exists an automatic transmission in which two clutches are provided in mutually different positions in the radial direction while overlapping each other in the axial direction, so as to make the automatic transmission compact, especially in the axial direction. In this automatic transmission, in the two clutches, either the input or output member is provided as a common member, and the other is provided as a separate member (see, for example, Japanese Patent Application Publication No. JP-A-H7-269665). In each of the two clutches, a large number of friction plates, an operating oil chamber that operates the friction plates, and a cancel oil chamber that cancels the centrifugal hydraulic pressure in the operating oil chamber are disposed so as to overlap one another in the axial direction.
Each of the two operating oil chambers and each of the two cancel oil chambers are provided in the corresponding one of the clutch drums, each of which is integrally structured with a turbine shaft. A hydraulic pressure is supplied to each of the two operating oil chambers via an oil hole formed in the corresponding one of the clutch drums. In particular, to the operating oil chamber that is positioned on the radially outer side, the hydraulic pressure is supplied via an oil passage that is independently formed on the outside of the clutch drum positioned on the radially inner side and an oil passage that is formed in the clutch drum positioned on the radially inner side.
Of the two cancel oil chambers, to the cancel oil chamber positioned on the radially inner side, oil is directly supplied via an oil hole formed in a boss portion of the clutch drum. To the cancel oil chamber positioned on the radially outer side, the oil stored in the cancel oil chamber that is positioned on the radially inner side is supplied via an oil passage provided in a piston of the clutch positioned on the radially inner side and via an oil passage provided in the clutch drum that is positioned on the radially inner side.